JP2005184269A - Method, device and program for measuring one way time lag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform end-to-end measurement containing a transmission lag in voice codec such that one device does not depend on the other device for measuring a one way time lag. <P>SOLUTION: A first communication terminal measures a time Δt1 (1) elapsing before the partner's measurement signal is received for the first time after the measurement signal is transmitted, and a time Δt1 (2) elapsing before the partner's second measurement signal is received after the measurement signal is transmitted. A second communication terminal measures a time Δt2 elapsing before the measurement signal is transmitted for the first time after the partner's measurement signal is received, calculates Ta (1) based on the difference between the Δt1 (1) and the Δt2, calculates Ta (2) based on the difference between the Δt1 (2) and the Δt2, selects Ta (1) or Ta (2) satisfying a relation 0<Ta<Ti as the reciprocation time lag T between communication terminals assuming the time interval for transmitting the measurement signal at the first communication terminal is Ti, and determines one way time lag td=T/2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a one-way delay time measuring method and a one-way delay time measuring apparatus.

  IP telephones using an IP (INTERNET PROTOCOL) network have attracted attention as access lines such as DSL become broadband.

  An IP telephone is a voice telephone service provided using IP network technology in part or all of a network.

  FIG. 1 shows an example of an IP telephone system. The IP telephone system in FIG. 1 includes telephones (TEL) 1 and 11, facsimiles (FAX) 2 and 12, private branch exchanges (PBX) 3 and 9 that accommodate telephones and facsimiles and other communication devices, and private branch exchanges and IP networks. VoIP (Voice over IP) gateways (GW) 4 and 8 that control the interface, routers 5 and 7 that control routing in the IP network, a gatekeeper 6 that manages the correspondence between telephone numbers and Internet addresses, and an IP network 10 ing.

  Each VoIP gateway may have a gatekeeper function.

  Here, a case where a telephone call is made from the telephone 1 to the telephone 11 will be described. A user of the telephone 1 dials a specific telephone number in order to make a call using the Internet. For example, “050-xxxxxxx” is dialed. Based on the “050”, the PBX 3 recognizes that the call from the telephone 1 is an IP telephone and connects to the VoIP gateway 4. The VoIP gateway 4 confirms the telephone number of the communication partner from the dialed “xxxxxxx” and inquires the gatekeeper 6 about the IP address corresponding to the dial number of the partner. Thereafter, when the VoIP gateway 4 obtains an IP address corresponding to the dial number of the other party from the gatekeeper 6, the VoIP gateway 4 executes a procedure for setting an IP connection with the other party's VoIP gateway 8. . As a result, a connection is established by the VoIP gateway 4 -router 5 -IP network 10 -router 7 -VoIP gateway 8. On the other hand, since the connection with the incoming telephone 11 is also made with the VoIP gateway 8, the outgoing telephone 1-home exchange 3-VoIP gateway 4-router 5-IP network 10-router 7-VoIP gateway 8-home exchange 9 -A connection will be set up in the route of the incoming telephone 11.

  Thereafter, the VoIP gateway 4 packetizes the voice signal from the telephone set 1 and transmits it to the IP network 10 via the router 5. The packetized voice data is transmitted to the VoIP gateway 8 of the communication partner via the IP network 10 and the router 7. The VoIP gateway 8 generates a voice signal from the received voice packet, and this voice signal is transmitted to the incoming telephone 11 via the indoor switch 9. Note that, between the VoIP gateways 4 and 8, for example, voice packets are transferred using RTP (Realtime Transport Protocol).

  Incidentally, various transmission delays occur in the transmission of the IP telephone system of FIG. For example, in the VoIP gateway 4, a delay of about 40 ms occurs for compressing voice data and a few ms for packetizing the voice data. In the router 5, a delay of about 200 ms at maximum occurs due to packet division and priority control processing. In addition, a transmission delay of about 10 ms occurs in the IP network 10, and a transmission wait of several ms occurs in the router 7. Further, in the VoIP gateway 8, a delay of about 200 ms is generated to absorb the fluctuation of the network by several ms for the expansion of the voice data. Note that “network fluctuation” means a state in which the arrival time of the packet is unstable on the receiving side, and the receiving side needs to accumulate and reproduce the arrived packet for a certain period of time. The time required for reproduction after accumulating for a certain period of time is the time required to absorb the fluctuation of the network.

  Further, according to the “Study Group Report on IP Network Technology”, the quality class of IP telephones is defined as shown in FIG. According to this, the total voice transmission quality rate (R value) is determined as follows for class A, which is communication quality equivalent to a fixed telephone, and class B and class C, communication quality equivalent to a mobile phone. .

Class A: R> 80
Class B: 80 ≧ R> 70
Class C: 70 ≧ R> 50
The end-to-end delay is also determined as follows.

Class A: Delay <100ms
Class B: 100 ms ≦ delay <150 ms
Class C: 150 ms ≦ delay <400 ms
Further, it is known that the overall voice transmission quality rate (R value) is defined by the type of codec and the one-way delay time.

  By the way, as a method for measuring a one-way delay time in a network, “time synchronization method” described in Patent Document 1 discloses a method for measuring a one-way delay time based on a response signal.

  A method for measuring the one-way delay time in Patent Document 1 will be described with reference to FIG. The master station a sends a count control signal for controlling the count operation of the signal reception time counter 20 provided in the slave station b to the slave station b. At the same time as sending this count control signal at time T 1, the master station a starts counting operation of the signal sending time counter 29. On the other hand, when the slave station b receives the count control signal from the master station a, the signal reception time counter 20 starts a count operation. When the slave station b sends a response signal to the master station a, the counting operation of the signal reception time counter 20 is finished. At this time, the slave station b returns the signal reception time indicated by the signal reception time counter 20, that is, “tr” to the master station a together with the response signal. When receiving the response signal from the slave station b, the master station a ends the counting operation of the signal transmission time counter 29. At this time, the signal transmission time counter 29 indicates the signal transmission time, that is, “ts”.

  The signal transmission time “ts” at the master station “a” and the signal reception time “tr” from the slave station “b” are sent to the delay time calculation circuit 28.

  By the way, since the bidirectionality of the transmission characteristic of the public telephone line has been demonstrated by Non-Patent Document 1 or Non-Patent Document 2, the delay time calculation circuit 28 is controlled by the master station a by the following equation (1). A delay time from the start of signal transmission until the slave station b receives the count control signal, that is, “td” is calculated.

td = (ts−tr) / 2 (1)
As a method for measuring a one-way delay time in a network, Patent Document 2 discloses a method for measuring a one-way delay time based on a return signal.

  A method of measuring the one-way delay time in Patent Document 2 will be described with reference to FIG. In response to an instruction from the delay time calculation circuit 31 of the main station 30, a predetermined signal for measuring the delay time is transmitted from the transmitter 33 to the slave station 35. This signal is received by the receiver 36 of the slave station 35 over time tA, and transmitted back from the transmitter 38 to the master station 30 over time tLP. In this case, the counter 37 of the slave station 35 measures the processing time tLP from when the signal is received by the receiver 36 of the slave station 35 until the signal is transmitted by the transmitter 38. The signal transmitted back from the slave station 35 is received by the receiver 34 of the master station 30 in time tB. On the other hand, the counter 32 measures the time tAB required for the receiver 34 to receive a predetermined signal for measuring the delay time from the transmitter 33 of the master station 30 via the slave station 35. Based on the measured time tLP and time tAB, the delay time calculation circuit 31 calculates the delay time td between the master station 30 and the slave station 35.

By the way, assuming that the times tAB, tA, tB, and tLP are tAB = tA + tB + tLP and the delay times tA and tB are equal as shown in FIG.
td (= tA = tB) = (tAB−tLP) / 2 (2)
Thus, the delay time td between the master station 30 and the slave station 35 is calculated.
JP-A-5-161181 JP-A-9-55740 Masanori Aida and two others, “Precise Time Comparison by Telephone Line” Radio Research Quarterly 1985, Vol. 160. P115-P124 Nakanobu Moritani and three others "Standard time supply system by public communication line" The Japan Watch Association 1992, No. 142. P1 to P16

  However, the one-way delay time measurement method described in Patent Document 1 and Patent Document 2 is a one-way delay time between a transmitter and a receiver, and the measured delay time includes compression of voice data in a VoIP gateway. There is a problem that delays such as delays in processing and packet processing of audio data are not included.

  Further, in the one-way delay time measuring method described in Patent Document 1, one-way delay time is measured based on a response signal, so one device depends on the other device, and the measurement in one device is performed. In the one-way delay time measuring method described in Patent Document 2, the one-way delay time is measured based on the loopback signal, so that the telephone line oscillates and sounds, etc. As a result, there is a problem that the measurement condition becomes worse due to an unstable state.

  The present invention has been made in view of the above problem, and one device does not depend on the other device to measure the one-way delay time, and the end-to-end including the transmission delay in the voice codec. It is an object of the present invention to provide a one-way delay time measuring method and a one-way delay time measuring apparatus that enable measurement.

  In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.

  The invention described in claim 1 is a one-way delay time measurement method between communication terminals that perform analog signal communication via a public telephone network, and a transmission step of transmitting a measurement analog signal from each of the communication terminals; Each of the communication terminals receives the measurement analog signal of the other party, and the first communication terminal that is one of the communication terminals transmits the measurement analog signal, The time Δt1 (1) until the measurement analog signal is received and the time Δt1 (2) from the time when the measurement analog signal is transmitted to the time when the second measurement analog signal is received are measured. And the second communication terminal, which is the other of the communication terminals, receives the measurement analog signal of the other party and then sends the measurement analog signal first. A measurement step for measuring the time Δt2 until transmission, Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, and Ta (2) is calculated based on the difference between Δt1 (2) and Δt2. When the time interval for transmitting the measurement analog signal in the first communication terminal is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2 satisfying 0 <Ta <Ti. ) As a round-trip delay time T between the communication terminals, and a calculation step for obtaining a one-way delay time td as td = T / 2.

  According to the first aspect of the present invention, it is possible to provide a one-way delay time measuring method in which one device does not depend on the other device to measure the one-way delay time. In addition, the one-way delay time can be measured without having to synchronize the time between one device side and the other device side.

  According to a second aspect of the present invention, there is provided a one-way delay time of the digital signal exchange network between a first communication terminal and a second communication terminal that perform analog signal communication via a digital signal exchange network that switches digital signals. In the measurement method, the first communication terminal transmits a measurement analog signal to the second communication terminal via a public telephone network, and the second communication terminal A second transmission step of transmitting a measurement analog signal to the first communication terminal via the digital signal exchange network; and the second communication step via the digital signal exchange network, the second communication step. A first reception step of receiving a measurement analog signal from the first communication terminal; and the second communication terminal receives the measurement analog signal from the first communication terminal via the public telephone network. A second reception step for transmitting, a time Δt1 (1) from when the first communication terminal transmits the measurement analog signal to when the first measurement analog signal is received, and the measurement A measurement step of measuring a time Δt1 (2) from when the analog signal is transmitted to when the second counterpart measurement analog signal is received; and at the second communication terminal, the counterpart measurement analog signal is A measurement step for measuring the time Δt2 from when the signal is received to when the measurement analog signal is first transmitted, Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, and Ta (2) is Δt1 When the time interval for transmitting the measurement analog signal in the first communication terminal is Ti and Ta is Ta (1) or Ta (2), the calculation is based on the difference between (2) and Δt2, and 0 < Ta <Ti A selection step of selecting Ta (1) or Ta (2) satisfying the condition as a round-trip delay time T between the communication terminals, and one way of the public line network between the first communication terminal and the second communication terminal When the delay time is td, ΔT21 = T−td is calculated, and the direction from the second communication terminal to the first communication terminal is between the first communication terminal and the second communication terminal. And calculating a one-way delay time ΔT21 of the digital signal switching network.

  According to the second aspect of the present invention, it is possible to provide an end-to-end one-way delay time measurement method including a transmission delay in a voice codec.

  According to a third aspect of the present invention, in the second aspect of the present invention, in place of the public telephone network, a network having a known one-way delay time between the first communication terminal and the second communication terminal is used. It is characterized by using.

  According to the third aspect of the present invention, it is possible to provide an end-to-end one-way delay time measurement method including a transmission delay in a voice codec.

  According to a fourth aspect of the present invention, there is provided a one-way delay time of the digital signal switching network between a first communication terminal and a second communication terminal that perform analog signal communication via a digital signal switching network that switches digital signals. In the measurement method, the first communication terminal transmits a measurement analog signal to the second communication terminal via the digital signal switching network, and the second communication terminal , A second transmission step of transmitting a measurement analog signal to the first communication terminal via a public line network, and the first communication terminal via the public line network, the second transmission step A first reception step of receiving a measurement analog signal from a communication terminal; and the second communication terminal receives a measurement analog signal from the first communication terminal via the digital signal switching network. A second reception step for transmitting, a time Δt1 (1) from when the first communication terminal transmits the measurement analog signal to when the first measurement analog signal is received, and the measurement A measurement step of measuring a time Δt1 (2) from when the analog signal is transmitted to when the second counterpart measurement analog signal is received; and at the second communication terminal, the counterpart measurement analog signal is A measurement step for measuring the time Δt2 from when the signal is received to when the measurement analog signal is first transmitted, Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, and Ta (2) is Δt1 When the time interval for transmitting the measurement analog signal in the first communication terminal is Ti and Ta is Ta (1) or Ta (2), the calculation is based on the difference between (2) and Δt2, and 0 < Ta <Ti A selection step of selecting Ta (1) or Ta (2) satisfying the condition as a round-trip delay time T between the communication terminals, and one way of the public line network between the first communication terminal and the second communication terminal When the delay time is td, ΔT12 = T−td is calculated and the direction from the first communication terminal to the second communication terminal is between the first communication terminal and the second communication terminal. And calculating a one-way delay time ΔT12 of the digital signal switching network.

  Further, in the invention described in claim 5, the one-way delay time of the network between the first communication terminal and the second communication terminal is known in place of the public telephone network in claim 4. It is characterized by using a network.

  According to the fourth and fifth aspects of the present invention, it is possible to provide a method for measuring the one-way delay time between the end and the end including the transmission delay in the voice codec.

  According to a sixth aspect of the present invention, in the one-way delay time measuring method according to any one of the first to fifth aspects, the measurement analog signal is a tone burst waveform.

  According to the sixth aspect of the present invention, since the measurement analog signal is a tone burst waveform, the time from the transmission of the measurement analog signal to the reception of the counterpart measurement analog signal in each of the communication terminals. Time can be measured easily.

  According to invention of Claim 7-9, the measuring apparatus suitable for implementation of said one way delay time measuring method is provided. Moreover, according to the invention of Claims 10-12, the program suitable for implementation of said one-way delay time measuring method is provided.

  As described above, according to the present invention, a one-way delay time measurement method including a transmission delay in a voice codec without one-way delay time being measured depending on the other device. In addition, a one-way delay time measuring device can be provided.

  Next, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
The first embodiment is a method for measuring the one-way delay time of a public line network. FIG. 5 shows a system to which the measurement method of the first embodiment is applied. The system shown in FIG. 5 includes a telephone set 16, a private branch exchange 17, a public line network 15, a private branch exchange 18, and a telephone set 19. The first embodiment is a method of measuring the one-way delay time between the telephone set 16 and the telephone set 19 in the system of FIG.

  The measurement principle will be described with reference to FIG. In the first embodiment, the one-way delay time is measured by transmitting a measurement analog signal (for example, using a 1 KHz sine wave (one cycle) tone burst waveform) to the telephone set 19 side. The time until the measurement analog signal is received from the telephone set 19 side and the time from the reception of the measurement analog signal from the telephone set 16 side to the transmission of the measurement analog signal to the telephone set 16 side are used. It is based on that. Note that measurement analog signals are transmitted to the other party at regular intervals on the telephone 16 side and the telephone 19 side.

  In FIG. 6, the time from when the measurement signal is transmitted on the telephone 16 side until reception of the counterpart measurement analog signal (hereinafter referred to as measurement signal) is Δt1, and the measurement signal is received on the telephone 19 side. Then, the time until the measurement signal is transmitted to the other party is Δt2, the transmission delay in the direction from the telephone set 16 to the telephone set 19 is Δtab, and the transmission delay in the direction from the telephone set 19 to the telephone set 16 is Δtba. Here, Δtab = Δtba can be considered due to the bidirectionality of the transmission characteristics of the public telephone line described above. Therefore, as is apparent from FIG. 6, the one-way delay time td between the communication terminals can be obtained by the following equation.

td = (Δt1−Δt2) / 2 (3)
It should be noted that the telephone 16 side and the telephone 19 side are not synchronized in time, whether the reception measurement signal B corresponds to the transmission measurement signal A, and the reception measurement signal D. It does not matter whether or not corresponds to the transmission measurement signal C. Accordingly, the time X and the time Y may be separated from each other to some extent, for example.

  However, transmission / reception of measurement signals may be as shown in FIG. 7A (case 1) and FIG. 7B (case 2). Case 1 is the case shown in FIG. 6, and Case 2 is a case where the measurement signal transmitted from the telephone set 19 side is transmitted before the telephone set 19 side receives the measurement signal used as a reference on the telephone set 16 side. This is a case where the telephone set 16 receives and transmits the above-mentioned reference measurement signal. In the case shown in FIGS. 7A and 7B, a 1 kHz sine wave (one cycle) is transmitted at 1000 ms intervals as a measurement signal on both the telephone 16 side and the 19 side. In case 1, a correct delay time of 125 ms can be calculated by the equation T = (Δt1−Δt2) / 2. In case 2, the correct delay time 125 ms can be calculated by the equation T = (Δt1 + Δt2 ′) / 2. Here, Δt2 and Δt2 ′ are times as shown in FIG.

  However, since it is difficult to distinguish between case 1 and case 2 in practice, both (Δt1 + Δt2 ′) / 2 and (Δt1−Δt2) / 2 are calculated and appropriate results are adopted. It will be. That is, in case 1, an appropriate result is adopted from 125 ms and 625 ms, but it is not known which is appropriate unless the delay time is predicted on the desk beforehand. In addition, if the delay time cannot be predicted on the desk, it is not possible to select an appropriate result.

  Therefore, in the present embodiment, the time from when the measurement signal serving as a reference is transmitted on the telephone 16 side to the time when the measurement signal is received from the telephone 19 side, and after the measurement signal is received on the telephone 19 side, The round-trip delay time is obtained by subtracting the time until the measurement signal is transmitted to the 16 side. However, as shown in FIG. 7, there are two cases, case 1 and case 2, and the calculation method is different for each case. This will be described with reference to FIGS. 8 and 9, the telephone 16 side is the A base, the telephone 19 side is the B base, the measurement signal transmission time interval (transmission cycle) at the A base is Tipa, and the measurement signal transmission time interval (transmission) at the B base. Period) is Tipb, the time from the measurement signal reception at the B site to the first measurement signal transmission is Δtb2, the time from the measurement signal transmission at the A site to the first measurement signal reception is Δta1 (1), and the A site Let Δta1 (2) be the time from measurement signal transmission to reception of the second measurement signal, and Ta be the round-trip delay time measured at the A site. Note that one half of the round trip delay time is the one way delay time.

  As shown in FIG. 8, in case 1, the correct round-trip delay time is calculated from Δta1 (1) −Δtb2 as shown in equation (1) of FIG. 8A and FIG. In case 2, the correct round-trip delay time is calculated from Δta1 (2) −Δtb2 as shown in FIG. 9A and equation (2) in FIG.

  In case 1, as shown in FIG. 8A, the time of the transmission waveform on the B base side is advanced by Δtb2 in the calculation, and the time difference (= 0) from the reception waveform from the A base is set. The time of the reception waveform from the base is advanced by Δtb2, and the time difference from the transmission waveform at the base A is set. This corresponds to a round trip delay time. That is, a process of making the phase times coincide in a pseudo manner is performed. FIG. 8B illustrates a waveform after the above processing is performed. Also in case 2, the same processing as in case 1 is performed as shown in FIGS. 9A and 9B. In case 1, however, Δtb2 is subtracted from Δta1 (1) at the A site, whereas in case 2, Δtb2 is subtracted from Δta1 (2) at the A site.

  Thus, since the calculation method differs depending on whether it is case 1 or case 2, in this embodiment, regardless of whether it is case 1 or case 2, (Δta1 (1) −Δtb2) Both (Δta1 (2) −Δtb2) are calculated, and a reasonable result is selected as the round trip delay time.

  Whether the result is valid is determined based on whether the result is positive and smaller than the transmission interval of the measurement signal. That is, assuming that the calculation result is Ta, the one satisfying 0 <Ta <Tipa is selected. Note that the transmission interval of the measurement signal is set to be equal to or greater than the maximum round-trip delay time.

  That is, as shown in FIG. 8, in case 1, both 650−400 = 250 ms and 1650−400 = 1250 ms are calculated, and 0 <250 <1000, so 250 ms is selected as the round trip delay time. In case 2, both 100−850 = −750 and 1100−850 = 250 ms are calculated, and 250 ms is selected as the round trip delay time. In this way, there are cases 1 and 2, but in the actual measurement, the calculation based on the above two formulas is performed without distinguishing between case 1 and case 2, and the one that satisfies the condition is selected. To do.

(Embodiment 2)
The second embodiment is a method of measuring the one-way delay time of the IP network that is the circuit under test using the one-way delay time of the public line network measured in the first embodiment. FIG. 10 shows a system to which the measurement method of the second embodiment is applied. The system shown in FIG. 10 includes a base A side device 40, a base B side device 50, a public line network 15, and an IP network 60. The site A side device 40 includes a telephone set 41, a private branch exchange 42, a VoIP gateway 43 and a router 44, and the site B side device 50 includes a telephone set 51, a private branch exchange 52, a VoIP gateway 53 and a router 54. Yes.

  The IP network 60 is a digital signal switching network that switches digital signals. However, since the digital signals include coded analog signals, the IP network 10 is a network that switches coded analog signals. It can be said. In addition, the telephone 41 and the telephone 51 are interfaced by a VoIP gateway or the like in the site A side device and the site B side device, and communicate with each other via a digital signal exchange network that switches digital signals. It is.

  By the way, with respect to the public line network, the measurement signal is directly supplied to the public line network from the private branch exchange 42 or the private branch exchange 52. In this case, the received measurement signal is directly supplied to the home switch 52 or the home switch 42. On the other hand, for the IP network, the measurement signal is transmitted from the router of each of the site A side device 40 and the site B side device 50, and this measurement signal is transmitted to the site A side device 40 and the site B side device 50. Each router receives it. Note that the measurement signal may be applied to the telephone by connecting a measuring device to be described later to the telephone, or may be applied directly to the private branch exchange 42 or the VoIP gateway 43. When the measurement signal is directly applied to the home exchange 42 or the VoIP gateway 43, the received measurement signal is supplied directly to the home exchange 42 or the VoIP gateway 43. By applying the measurement signal to the telephone and acquiring the received measurement signal from the telephone, the one-way delay through all the devices in the network and the base can be measured.

  The measurement signal from the site A side device 40 is transmitted to the site B side device 50 via the public line network 15, and the site B side device 50 receives this measurement signal. The measurement signal from the site B side device 50 is transmitted to the site A side device 40 via the IP network 60, and the site A side device 40 receives this measurement signal.

  The second embodiment uses the one-way delay time (Δtab) of the public line network measured in the first embodiment in the system of FIG. 10, and the one-way delay time of the IP network 60 in the direction from the telephone 51 to the telephone 41. This is a method of measuring (ΔTba).

  In the measurement, the difference from the first embodiment is that in the first embodiment, both the bases A and B transmit the measurement signal via the public network, whereas in the second embodiment, the measurement signal from the base A. Is transmitted via the public line network 15, and the measurement signal at the base B is transmitted via the IP network 60.

  As in the first embodiment, the round-trip time calculation method calculates both Δta1 (1) −Δtb2 and Δta1 (2) −Δtb2, and selects the one that satisfies 0 <Ta <Tipa. If the round-trip time is obtained as Ta, the one-way delay time Ta-Th via the IP network can be calculated by subtracting the known one-way delay time Th of the public network from Ta.

In FIG. 10, if the measurement signal is transmitted from the A site via the IP network 60 and the measurement signal is received from the B site via the public telephone network, the IP network in the direction from the A site to the B site. 60 one-way delay times Tba can be obtained. Further, as shown in FIG. 11, a measurement signal may be transmitted from the B base.
(measuring device)
FIG. 12 shows a configuration example of the delay time measuring apparatus used in each of the above embodiments. Since the delay time measuring device on the A site side and the delay time measuring device on the B site side have the same configuration, the delay time measuring device on the A site side will be described.

  As shown in FIG. 12, the delay time measuring apparatus according to the present embodiment generates a data input unit 111 and a data output unit 112 that input and output data, a control unit 113 that controls each unit, and a measurement signal. A tone burst waveform generator 114, a waveform transmitter 115 for transmitting the generated waveform, a bidirectional communication line such as a public telephone line for transmitting a measurement signal, and a non-bidirectional communication line such as an IP network A switch for switching between, a threshold detection unit 117 for detecting a transmission signal waveform, a bidirectional communication line such as a public telephone line for receiving a measurement signal, and a non-bidirectional communication line such as an IP network Switch 118 for switching, waveform receiver 119 for receiving a measurement signal, threshold detector 120 for detecting a received signal waveform, and detecting a phase time difference between a received signal and a transmitted signal A phase time difference detection unit 121, a measurement data reception unit 122 that transmits and receives measurement data via a measurement data transfer communication line, a measurement data transmission unit 123, and a transmission signal and a reception signal detected by the phase time difference detection unit 121 Is provided with a delay time calculation unit 124 that calculates a one-way delay time using the time difference between the two and the received measurement data.

  This delay time measuring apparatus is connected to, for example, a telephone for telephone calls via a public telephone line network and a telephone for telephone calls via an IP network, and transmits a measurement signal via the public telephone line network or via the IP network. Further, the switches 116 and 118 are switched as appropriate depending on whether the reception is made via the public telephone line network or the IP network.

  Further, the delay time measuring apparatus can be realized by installing a program for processing each functional unit of the delay time measuring apparatus shown in FIG. 12 in a computer such as a PC. Each functional unit can be configured by hardware.

  Next, the processing operation of the delay time measuring apparatus will be described with reference to the flowchart of FIG. The flowchart shown in FIG. 13 is for measuring the delay time of a bidirectional line such as a public line network.

  In FIG. 13, the transmission time interval (transmission cycle) of the measurement signal at the A site is Tipa, the transmission time interval (transmission cycle) of the measurement signal at the B site is Tipb, and for the first measurement from the reception of the measurement signal at the A site. The time until signal transmission is Δta2, the time from reception of the measurement signal at the B site to the first measurement signal transmission is Δtb2, and the time from measurement signal transmission at the A site to the reception of the first measurement signal is Δta1 (1). , Δta1 (2) is the time from the measurement signal transmission at the A site to the second measurement signal reception, Δtb1 (1) is the time from the measurement signal transmission at the B site to the first measurement signal reception, Δtb1 (2) is the time from the measurement signal transmission to the second measurement signal reception at Ta, and the round trip delay time measured at the A site is Ta, and the time is measured at the B site. The delay time and Tb.

  In FIG. 13, the processing on the A site side and the processing on the B site side are substantially the same, so the processing on the A site side will be described.

  First, condition data (Tipa) is input from the data input unit 111 (step 1). Further, the measurement signal is transmitted from the waveform transmission unit 115 to the site B via the bidirectional line (step 2), and the waveform reception unit 119 receives the measurement signal via the bidirectional line. (Step 3).

  Based on these transmission / reception signals, Δta2 is measured (step 4), and is transmitted from the measurement data transmission unit 123 to the base B (step 5). Also, Δtb2 data is received from the B base (step 6). Further, Δta1 (1) and Δta1 (2) are measured (step 7), and Ta (1) = Δta (1) −Δtb2 and Ta (2) = Δta1 (2) −Δtb2 are calculated by the delay time calculation unit 124. (Step 8). If 0 <Ta (1) <Tipa is satisfied, Ta (1) is determined as the round trip delay time Ta (steps 9 and 11). If 0 <Ta (1) <Tipa is not satisfied, it is checked whether 0 <Ta (2) <Tipa is satisfied. If satisfied, Ta (2) is determined as the round trip delay time Ta (step 10). 11). Then, a one-way delay time Th = Ta / 2 is obtained (step 12). If 0 <Ta (2) <Tipa is not satisfied, Δta1 (1) and Δta1 (2) are measured again, and the above process is repeated.

  Next, delay time measurement processing for a non-bidirectional line such as an IP network will be described with reference to the flowchart of FIG. Here, Th obtained as described above is used. Tab is the one-way delay time of the non-bidirectional line in the direction from the A base to the B base, and Tba is the one-way delay time of the non-bidirectional line in the direction from the B base to the A base.

  In FIG. 14, the processing at the A site side and the processing at the B site side are substantially the same, so the processing at the A site side will be described.

  First, condition data (Tipa, Th, measurement direction of non-bidirectional line: A-> B or B-> A) is input from the data input unit 111 (step 21).

  When the measurement direction is A-> B, a measurement signal is transmitted from the waveform transmitter 115 to the B site side via the non-bidirectional line (step 23), and measured from the B site via the bidirectional line. A service signal is received (step 24). If the measurement direction is B-> A, a measurement signal is transmitted to the site B via the bidirectional line (step 25), and the measurement signal is transmitted from the site B via the non-bidirectional line. A signal is received (step 26).

  Based on these transmission / reception signals, Δta2 is measured (step 27), and is transmitted from the measurement data transmission unit 123 to the B base. Further, Δtb2 data is received from the B base (step 29). Further, Δta1 (1) and Δta1 (2) are measured (step 30), and Ta (1) = Δta (1) −Δtb2 and Ta (2) = Δta1 (2) −Δtb2 are calculated (step 31). If 0 <Ta (1) <Tipa is satisfied, Ta (1) is determined as the round-trip delay time Ta (steps 32 and 34). If 0 <Ta (1) <Tipa is not satisfied, it is checked whether 0 <Ta (2) <Tipa is satisfied. If satisfied, Ta (2) is determined as the round trip delay time Ta (step 33). 34). Then, the one-way delay time Tab or Tba = Ta-Th is obtained (step 35). If 0 <Ta (2) <Tipa is not satisfied, Δta1 (1) and Δta1 (2) are measured again and the above process is repeated.

(Other examples of measuring devices)
Instead of the configuration of the delay time measuring apparatus as described above, the following configuration may be used.

  FIG. 15 shows an example of a block diagram of this configuration. The block diagram of FIG. 15 includes oscillators 71 and 81, transmission circuits 72, 75, 82 and 85, reception circuits 73, 76, 83 and 86 and oscilloscopes 74 and 84.

  The measurement signals are generated by the oscillators 71 and 81, and the time from when the measurement signals are transmitted by the oscilloscopes 74 and 84 to when the other measurement signal is received is measured. In addition, the time from when the measurement signal is received until the measurement signal is transmitted to the other party is also measured. Moreover, it has two transmission lines, one is a bidirectional line such as a public network, and the other is a non-bidirectional line such as an IP network, and both can be switched. Further, the transmission circuit and the reception circuit are configured as a telephone, for example. The data measured on one side can be transmitted to the other side by e-mail or the like, for example. Then, the one-side delay time can be obtained by performing the calculation according to the method described so far.

  FIG. 16 shows an example of a circuit connected to the telephone or the like on one side in the configuration of FIG. The circuit in FIG. 16 includes an oscillator 90, amplifiers (AMP) 91 and 92, an oscilloscope 93, transformers 94 to 98, and switches 101 to 104.

  In the circuit of the measuring apparatus of FIG. 16, a sine wave signal that is a measurement signal generated by the oscillator 90 is transmitted on the Lch via the transformer 96 by closing the switch 101. Similarly, a sine wave signal that is a measurement signal generated by the oscillator 90 is transmitted on the Rch via the transformer 95 by closing the switch 102.

  The signal received on the Lch via the transformer 97 is supplied to the Lch terminal of the oscilloscope by connecting the switch 104 to the lower contact X. Similarly, the signal received on Rch via the transformer 98 is supplied to the Rch terminal of the oscilloscope by connecting the switch 103 to the lower contact X.

The signal transmitted on the Lch is turned back by connecting the switch 104 to the upper contact Y and supplied to the Lch terminal of the oscilloscope. Similarly, the signal transmitted on the Rch is turned back by connecting the switch 103 to the upper contact Y and supplied to the Rch terminal of the oscilloscope.
(Usage example of measuring device)
A usage example when the circuit of the measuring apparatus of FIG. 16 is used in the first embodiment will be described.

  In the setting on the telephone 16 side in the first embodiment, the switch 101 is closed and a measurement signal on Lch is transmitted to the telephone 19 side. Further, by connecting the switch 104 to the upper contact Y, the measurement signal on the Lch is turned back and supplied to the Lch terminal of the oscilloscope. Further, the switch 102 is opened and the measurement signal on Rch is not transmitted. Further, by connecting the switch 103 to the lower contact X, the measurement signal on the Rch telephone 19 side is received and supplied to the Rch terminal of the oscilloscope.

  As the oscillator 90, a 1 KHz tone burst waveform (1: 999 / sine wave) generated by a PC (PERSONAL COMPUTER) can be used.

  The oscilloscope 93 simultaneously displays the transmitted measurement signal on the Lch and the received measurement signal on the Rch, and based on the phase difference between the folded measurement signal on the Lch and the received measurement signal on the Rch. Then, visually measure the time from when the measurement signal is transmitted until the other party's measurement signal is received.

  In the setting on the telephone 19 side in the first embodiment, the switch 101 is opened and the measurement signal on the Lch is not transmitted. Further, by connecting the switch 104 to the lower contact point X, a measurement signal on the Lch is received and supplied to the Lch terminal of the oscilloscope. Further, the switch 102 is closed, and the measurement signal on Rch is transmitted to the telephone set 16 side. Further, by connecting the switch 103 to the upper contact Y, the measurement signal on the telephone 19 side on the Rch is folded and supplied to the Rch terminal of the oscilloscope.

  The oscilloscope 93 simultaneously displays the transmitted measurement signal on the Rch and the received measurement signal on the Lch, and based on the phase difference between the folded measurement signal on the Rch and the received measurement signal on the Lch. Then, visually measure the time from when the measurement signal is received to when the measurement signal is received by the other party.

  Further, the setting in the second embodiment can also be set according to the setting on the telephone 16 side and the telephone 19 side, only by the line on which the measurement signal is transmitted.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made within the scope of the claims.

It is a figure for demonstrating the structural example of an IP telephone system. It is a figure for demonstrating the quality class of IP telephone. It is FIG. (1) for demonstrating the method to measure the one-way delay time in the past. It is FIG. (2) for demonstrating the method to measure the one-way delay time in the past. This is a system to which the measurement method of the first embodiment is applied. 4 is a diagram for explaining a measurement principle in Embodiment 1. FIG. 4 is a diagram for explaining a measurement principle in Embodiment 1. FIG. It is a figure for demonstrating the measurement principle in Embodiment 1 (case 1). It is a figure for demonstrating the measurement principle in Embodiment 1 (case 2). This is a system to which the measurement method of the second embodiment is applied. This is a system to which the measurement method of the second embodiment is applied. It is a structural example of a delay time measuring apparatus. It is a flowchart of the delay time measurement of a bidirectional line. It is a flowchart of delay time measurement of a non-bidirectional line. It is a figure for demonstrating the example of another measuring apparatus. It is a figure for demonstrating the example of the circuit of another measuring apparatus.

Explanation of symbols

1, 11, 16, 19, 41, 51 Telephone 2, 12 FAX
3, 9, 17, 18, 42, 52 Private branch exchange (PBX)
4, 8, 43, 53 VoIP
5, 7, 44, 54 Router 10, 60 IP network 15 Public network 40 Base A side device 50 Base B side device 71, 81, 90 Oscillator 72, 75, 82, 85 Transmitting circuit 73, 76, 83, 86 Circuit 74, 84, 93 Oscilloscope 91, 92 Amplifier (AMP)
94, 95, 96, 97, 98 Transformer 101, 102, 103, 104 Switch 111, 211 Data input unit 112, 212 Data output unit 113, 213 Control unit 114, 214 Tone burst waveform generation unit 115, 215 Waveform transmission unit 116, 216 Switch 117, 217 Threshold detector 118, 218 Switch 119, 219 Waveform receiver 120, 220 Threshold detector 121, 221 Phase time difference detector 122, 222 Measurement data receiver 123, 223 Measurement data transmitter 124, 224 Delay time calculator

Claims (12)

In a one-way delay time measurement method between communication terminals that perform analog signal communication via a public telephone network,
A transmitting step of transmitting an analog signal for measurement from each of the communication terminals;
In each of the communication terminals, a receiving step of receiving an opponent measurement analog signal;
In the first communication terminal which is one of the communication terminals, a time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the measurement analog signal A measurement step of measuring a time Δt1 (2) from when the signal is transmitted to when the second counterpart measurement analog signal is received;
A measurement step of measuring a time Δt2 from when the other measurement analog signal is received until the first measurement analog signal is transmitted in the second communication terminal which is the other of the communication terminals;
Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and an analog signal for measurement is transmitted at the first communication terminal. When the time interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is set as the round-trip delay time T between the communication terminals. A selection step to select;
A one-way delay time measuring method, wherein the one-way delay time td is calculated as td = T / 2. In the one-way delay time measuring method for the digital signal switching network between the first communication terminal and the second communication terminal that perform analog signal communication via the digital signal switching network that switches the digital signal,
A first transmission step in which the first communication terminal transmits a measurement analog signal to the second communication terminal via a public telephone network;
A second transmission step in which the second communication terminal transmits an analog signal for measurement to the first communication terminal via the digital signal switching network;
A first receiving step in which the first communication terminal receives a measurement analog signal from the second communication terminal via the digital signal switching network;
A second receiving step in which the second communication terminal receives the measurement analog signal from the first communication terminal via the public telephone network;
In the first communication terminal, a time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and after the measurement analog signal is transmitted, 2 A measurement step for measuring a time Δt1 (2) until the measurement partner's measurement analog signal is received;
In the second communication terminal, a measurement step of measuring a time Δt2 from the reception of the partner measurement analog signal to the first transmission of the measurement analog signal;
Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and an analog signal for measurement is calculated at the first communication terminal. When the transmission time interval is Ti and Ta is Ta (1) or Ta (2), the round-trip delay time T between the communication terminals is set to Ta (1) or Ta (2) satisfying 0 <Ta <Ti. A selection step to select as,
When the one-way delay time of the public line network between the first communication terminal and the second communication terminal is td, ΔT21 = T−td is calculated and the first communication terminal calculates the first communication terminal from the second communication terminal. A one-way delay time measuring method comprising: calculating a one-way delay time ΔT21 of the digital signal switching network between the first communication terminal and the second communication terminal in the direction of the communication terminal.   3. The one-way delay time measuring method according to claim 2, wherein a network having a known one-way delay time between the first communication terminal and the second communication terminal is used instead of the public telephone network. . In the one-way delay time measuring method for the digital signal switching network between the first communication terminal and the second communication terminal that perform analog signal communication via the digital signal switching network that switches the digital signal,
A first transmission step in which the first communication terminal transmits a measurement analog signal to the second communication terminal via the digital signal switching network;
A second transmission step in which the second communication terminal transmits a measurement analog signal to the first communication terminal via a public network;
A first receiving step in which the first communication terminal receives an analog signal for measurement from the second communication terminal via the public network;
A second receiving step in which the second communication terminal receives the measurement analog signal from the first communication terminal via the digital signal switching network;
In the first communication terminal, a time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and after the measurement analog signal is transmitted, 2 A measurement step for measuring a time Δt1 (2) until the measurement partner's measurement analog signal is received;
In the second communication terminal, a measurement step of measuring a time Δt2 from the reception of the partner measurement analog signal to the first transmission of the measurement analog signal;
Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and an analog signal for measurement is calculated at the first communication terminal. When the transmission time interval is Ti and Ta is Ta (1) or Ta (2), the round-trip delay time T between the communication terminals is set to Ta (1) or Ta (2) satisfying 0 <Ta <Ti. A selection step to select as,
When the one-way delay time of the public line network between the first communication terminal and the second communication terminal is td, ΔT12 = T−td is calculated and the second communication terminal calculates the second And calculating the one-way delay time ΔT12 of the digital signal switching network between the first communication terminal and the second communication terminal in the direction of the communication terminal.   5. The one-way delay time measuring method according to claim 4, wherein a network having a known one-way delay time between the first communication terminal and the second communication terminal is used instead of the public telephone network. .   6. The one-way delay time measuring method according to claim 1, wherein the measurement analog signal is a tone burst waveform. In a one-way delay time measuring device for measuring a one-way delay time between communication terminals that perform analog signal communication via a public telephone network,
A transmission means for transmitting an analog signal for measurement at regular time intervals;
Receiving means for receiving the other party's measurement analog signal;
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted Measuring means for measuring the time Δt1 (2) until receiving
Data receiving means for receiving, from the counterpart side, a time Δt2 from the reception of the measurement analog signal at the counterpart side until the first transmission of the measurement analog signal;
Time for calculating Ta (1) based on the difference between Δt1 (1) and Δt2, calculating Ta (2) based on the difference between Δt1 (2) and Δt2, and transmitting the measurement analog signal in the transmission means When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. And a one-way delay time measuring apparatus, wherein the one-way delay time td is calculated as td = T / 2. In the one-way delay time measuring device for measuring the one-way delay time of the digital signal exchange network between communication terminals that communicate analog signals via a digital signal exchange network that switches digital signals,
A transmission means for transmitting measurement analog signals at regular time intervals via a public telephone network;
Receiving means for receiving the other party's measurement analog signal via the digital signal exchange network;
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted Measuring means for measuring the time Δt1 (2) until receiving
Data receiving means for receiving, from the counterpart side, a time Δt2 from the reception of the measurement analog signal at the counterpart side until the first transmission of the measurement analog signal;
Time for calculating Ta (1) based on the difference between Δt1 (1) and Δt2, calculating Ta (2) based on the difference between Δt1 (2) and Δt2, and transmitting the measurement analog signal in the transmission means When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. When the one-way delay time of the public line network between the communication terminals is td, ΔT21 = T−td is calculated, and the direction from the partner side to the one-way delay measuring device side is calculated between the communication terminals. A one-way delay time measuring apparatus, comprising: calculating means for obtaining a one-way delay time ΔT21 of the digital signal switching network. In the one-way delay time measuring device for measuring the one-way delay time of the digital signal exchange network between communication terminals that communicate analog signals via a digital signal exchange network that switches digital signals,
Transmission means for transmitting the measurement analog signal at regular time intervals via the digital signal switching network;
Receiving means for receiving the other party's measurement analog signal via the public network;
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted Measuring means for measuring the time Δt1 (2) until receiving
Data receiving means for receiving, from the counterpart side, a time Δt2 from the reception of the measurement analog signal at the counterpart side until the first transmission of the measurement analog signal;
Time for calculating Ta (1) based on the difference between Δt1 (1) and Δt2, calculating Ta (2) based on the difference between Δt1 (2) and Δt2, and transmitting the measurement analog signal in the transmission means When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. When the one-way delay time of the public line network between the communication terminals is td, ΔT12 = T−td is calculated, and the direction from the one-way delay measuring device side to the partner side is determined between the communication terminals. A one-way delay time measuring apparatus, comprising: calculating means for obtaining a one-way delay time ΔT12 of the digital signal switching network. In a program for causing a computer to execute processing for measuring a one-way delay time between communication terminals that perform analog signal communication via a public telephone network,
A transmission procedure for transmitting measurement analog signals at regular time intervals;
Reception procedure for receiving the other party's measurement analog signal,
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted A measurement procedure for measuring time Δt1 (2) until reception of
A data reception procedure for receiving a time Δt2 from the reception of the measurement analog signal on the counterpart side until the first transmission of the measurement analog signal from the counterpart side;
Time when Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and the measurement analog signal is transmitted in the transmission procedure. When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. And a calculation procedure for calculating the one-way delay time td as td = T / 2. A program for causing a computer to execute a process for measuring a one-way delay time of the digital signal exchange network between communication terminals that perform analog signal communication via a digital signal exchange network that switches digital signals,
A transmission procedure for transmitting measurement analog signals at regular time intervals via the public telephone network,
A receiving procedure for receiving the other party's measurement analog signal via the digital signal exchange network;
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted A measurement procedure for measuring time Δt1 (2) until reception of
A data reception procedure for receiving a time Δt2 from the reception of the measurement analog signal on the counterpart side until the first transmission of the measurement analog signal from the counterpart side;
Time when Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and the measurement analog signal is transmitted in the transmission procedure. When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. When the one-way delay time of the public line network between the communication terminals is td, ΔT21 = T−td is calculated, and the communication terminal in the direction from the partner side to the computer side where the program is installed And a calculation procedure for obtaining a one-way delay time ΔT21 of the digital signal switching network between the computers. A program for causing a computer to execute processing for measuring a one-way delay time of the digital signal switching network between communication terminals that perform communication of analog signals via a digital signal switching network that switches digital signals,
A transmission procedure for transmitting an analog signal for measurement at regular time intervals via the digital signal switching network;
A receiving procedure for receiving the other party's measurement analog signal via the public network,
The time Δt1 (1) from when the measurement analog signal is transmitted until the first measurement analog signal is received, and the second measurement analog signal after the measurement analog signal is transmitted A measurement procedure for measuring time Δt1 (2) until reception of
A data reception procedure for receiving a time Δt2 from the reception of the measurement analog signal on the counterpart side until the first transmission of the measurement analog signal from the counterpart side;
Time when Ta (1) is calculated based on the difference between Δt1 (1) and Δt2, Ta (2) is calculated based on the difference between Δt1 (2) and Δt2, and the measurement analog signal is transmitted in the transmission procedure. When the interval is Ti and Ta is Ta (1) or Ta (2), Ta (1) or Ta (2) satisfying 0 <Ta <Ti is selected as the round-trip delay time T between the communication terminals. When the one-way delay time of the public line network between the communication terminals is td, ΔT12 = T−td is calculated, and the communication terminal in the direction from the computer side on which the program is installed to the partner side is calculated. And a calculation procedure for obtaining a one-way delay time ΔT12 of the digital signal switching network between the computers.

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